In general, a seat in a vehicle is largely composed of a seatback supporting the passenger's back and a seat cushion supporting the part of the passenger from the hip to the thigh, in which the angle of the seatback can be adjusted by the reclining device.
Further, the reclining device includes left and right recliners each disposed to the left and right sides of the seat and a connecting shaft of which both ends are connected with the left and right recliners by splines to connect the left and right recliners.
The connecting shaft can be rotated by a driving force transmitted from an electric motor (not shown).
On the other hand, it is preferable to minimize the size and thickness of the reclining device in consideration of the seat because the reclining device is disposed the connecting portion of the seatback and the seat cushion.
However, decreasing the size of the reclining device decreases the engagement strength between geared parts and backlash is caused in stopping the reclining device, such that the seatback rocks back and forth or, if excessive, the reclining of the seatback unexpectedly operates, which threatens the passenger's safe. Accordingly, researches to prevent these problems are being made in recent years.